Electrical machine, the magnetic circuit of which comprises one or more permanent magnets



Dec. 18, 1956 M. F. REYNST ET AL 2,774,895

ELECTRICAL MACHINE, THE MAGNETIC CIRCUIT OF WHICH COMPRISES ONE OR MORE PERMANENT MAGNETS Filed Dec. 6, 1952 INVENTORS MAXIMIEEN ,FELIX REYNST ROBERT HENRI DE BEER AGENT United States Patent O ELECTRICAL MACHINE, THE MAGNETIC CIR- CUIT OF WHICH COMPRISES ONE OR MORE PERMANENT MAGNETS Maximilien ran Rcynst and Robert Henri de Beer, Eindhoven, Netherlands, assignors to Hartford National Bank and Trust Company, Hartford, Conn., as trustee Application December 6, 1952, Serial No. 324,524

Claims priority, application Netherlands December 29, 1951 8 Claims. (Cl. 310-403) The invention relates to an electrical machine, the magnetic circuit of which comprises one or more permanent magnets, the rotor and the stator being arranged side by side in an axial direction, separated by an air gap, the direction of magnetisation of the magnet being parallel to the said axial direction and is characterised in that the magnet is shaped in the form of a disc and magnetized in the direction of the smallest dimension and is made of a material having a comparatively high coercive force and being substantially not demagnetisable, disc-shaped pole shoes of soft magnetic material being arranged in the axial direction at the side of the comparatively large pole surface of the magnet, the thickness of these pole shoes increasing preferably towards the winding, which is provided on a narrowed part between two pole shoes. Thus a fiat shape and a rugged construction of the machine may be obtained in a simple manner, whilst, owing to the concentration of the flux in the narrowed portion inside the winding, adequate inductance is obtainable in spite of the large pole surfaces of the permanent magnets generally required. Owing to the smallcore diameter of the winding, the mean length of the turns is small, so that the copper losses are also low, which is conducive to the output.

The term substantially not demagnetisable or substantially non-demagnetizable is to be understood to mean herein that, after having been removed from the magnetizing apparatus the magnet is substantially not demagnetized without the need of any precautions, such for example as the conventional measure of applying a short-circuiting circuit of soft iron between the north pole and the south pole prior to the removal, the magnet thus resuming substantially its working point Br (remanence), upon being included again subsequently in a closed iron circuit. The aforesaid term is, moreover, to be understood to mean, more particularly, that no appreciable demagnetisation occurs, if two identical magnets are joined outside a magnetic circuit with their corresponding poles upon one another and then separated again from one another. Included in a closed soft-iron circuit the magnet will also in this case resume substantially its working point Br, which means that in a definite condition of loading a generator has a constant voltage and a motor a substantially constant speed of rotation.

The said materials fulfill, in general, the condition that the ratio remanence Br to coercive force BHC should be lower than 4, preferably lower than 2.

According to a further feature of the invention the aforesaid permanent-magnetic material has a BHmax value of O.7 1O

Materials particularly suitable for this purpose are described in a British Patent No. 708,127.

These materials consist primarily of non-cubic crystals of poly-oxides of Fe and at least one of the metals Ba, Sr, Pb, and, if necessary, Ca, more particularly, of simple and/or mixed crystals having the structure of portant.

magneto-plumbite, of the composition Me'O.6Fe2O3, wherein Me designates one of the metals Pb, Ba or Sr. Such material may have a ratio of B): to BHC of 2000:1640=about 1.2 with a value BHmax of about 0.8 10 In times of scarcity of raw material these materials, which do not contain C0 or Ni, are very im- These materials have, moreover, a comparatively high resistance of at least 10 ohm-cm. for example, 3X10 ohm-cm., so that the machine may be particularly suitable for use with high frequencies, particularly if also the parts of weak magnetic material exhibit low losses. In spite of the large volume that would be obtained with the use of these materials, having a comparatively low BHmax value of, for example, 1x10 compared with the use of the known modern magnet rods, reasonable Weights are obtainable owing to the low specific weight.

In order that the invention may be readily carried into effect, it will now be described in detail with reference to the accompanying drawing, in which:

Fig. 1a is a cross-sectional view of a machine in accordance with the invention;

Fig. 1b is a plan view of the permanent magnet contained in the construction illustrated in Fig. 1a;

Fig. 1c is a plan view of the soft magnetic portion of the construction illustrated in Fig. la;

Fig. 2 is a cross-sectional view of a further embodiment of a machine according to the invention;

Fig. 3 is a plan View of a permanent magnet which may be used in the constructions illustrated in Figs. 1a and 2;

Figs. 4a and 4b are plan and cross-sectional views respectively of a soft ferromagnetic portion which may be employed in the constructions illustrated in Figs. 1a and 2;

Figs. 5a and 5b are plan and side views respectively of a modification of the soft ferromagnetic portion illustrated in Fig. 4;

Figs. 6a and 6b are plan and side views respectively of a permanent magnet which may be used in a machine according to the invention.

Fig. 1 shows a machine according to the invention. The magnets 1 and 2 of a material, which is substantially not demagnetisable, are shaped in the form of discs, magnetized in the direction of the smallest dimension 5, i. e., in their thickness direction, and seated on a shaft 6. Parts 7 (Fig. 1b) of non-magnetic material may be provided between the two magnets. In an axial direction at the side of the pole surfaces of the magnets 1 and 2 provision is made of the disc-shaped pole shoes 3 and 4 'of soft magnetic material, the thickness of which (Fig. 1a) increases towards the winding 8. The winding 8 is arranged on a narrowed part 9. On the other side of the magnets a similar combination of pole shoes 10 and 11 and a winding 12 is provided, so that a double construction is obtained. Use may be made of a rotatable arrangement of the magnets, or, as an alternative, of the pole shoes combinations or, as a further alternative, of both of them.

The course of the flux is indicated by a broken line.

Fig. 2 shows the two pole shoe combinations combined with a single coil 13; four magnets 14 to 17 are provided on each side of the pole shoes. Owing to the greater quantity of magnet steel a higher output may be produced and the single coil yields advantages. In order to reduce the reluctance, use may be made of two plates 18 of soft magnetic material.

Fig. 3 shows four magnets 19 to 22 arranged in the same plane symmetrically about the shaft 6. By using such a magnet system in a generator as shown in Figs. 1 and 2 the frequency may be doubled at the same speed of rotation. When using the aforesaid materials there is 3 no objection against the arrangement shown of the magnets with the sides of the unlike poles N and S against one another, although a slight reduction of the stray losses is obtained by an arrangement having a suitable intermediate space.

Fig. 4a is a side view and Fig. 4b a sectional view of an embodiment in which four pole shoes 23 to 26 are combined with four coils 27 to 30. This combination may also be arranged in a manner similar to that shown in Figs. 1 and 2 or be combined with a magnet system as shown in Fig. 3.

Instead of using four pole shoes with four coils, use may, as an alternative, be made of three, five or more poles with coils, if desired in conjunction with three, five or more magnets.

If the soft magnetic material is a material having a high electrical resistance of preferably at least 10 ohm-cm, these machines are particularly suitable for use with high frequencies.

Fig. 5a is a plan view and Fig. 5b a lateral view of an embodiment differing from that shown in Fig. 4.

The windings 27 to 30 are also in this case partly countersunk and arranged, about an annular body 31. Each winding embraces a core which is indicated in Fig. 5b by the broken lines 32. The pole shoes provided between two successive windings, for example, between 29 and 30 become gradually thinner, starting from a core, up to the line 33, then they become thicker up to the next following core, which is shown in Fig. 5b. In such an embodiment the ring 31 may be made of concentrical laminations (if desired in the form of wound tape), as is shown in part in Fig. 5a and designated by 34. Consequently the flux enters and leaves the pole shoes at the side edges of the laminations and need not traverse the insulation between the laminations.

Figs. 6a and 6b are a plan view and a lateral view of a magnetic system comprising only one permanent magnet 35, the south poles 36 being made of soft magnetic material and having a plate-shaped part 37, which is adjacent the south pole of the magnet 35.

What we claim is:

1. Electrical apparatus comprising axially-arranged, axial air-gap spaced rotor and stator members, one of said members, including a flat permanent magnet portion mounted at right angles to the axes of the members and magnetized in its thickness direction and thus parallel to the axes of the members to produce pole surfaces, said permanent magnet portion being constituted of a high coercive force material and being substantially nondemagnetizable, the other of said members comprising a substantially flat member of soft ferromagnetic material mounted at right angles to the axes of said members and adjacent a pole surface of the permanent magnet portion, and a winding on a reduced portion of said soft ferromagnetic member, said soft ferromagnetic member having a portion intermediate said reduced portion and a portion remote therefrom of greater thickness than said reduced and remote portions, said rotor and stator members being rotatable relative to one another about their axes whereby interaction may accur between the field produced by the permanent magnet and the winding on the soft ferromagnetic member.

2. Electrical apparatus as set forth in claim 1 wherein the high coercive force material consists essentially of non-cubic crystals having a magnetoplumbite structure and a formula MeO-GFezOs, where Me designates a metal selected from the group consisting of Pb, Ba and Sr, and the soft ferromagnetic member is constituted of material exhibiting an electrical resistance in excess of ohm-cm.

3. Electrical apparatus comprising axially-arranged, axial air-gap spaced rotor and stator members, one of said members comprising a fiat permanent magnet portion mounted at right angles to the axes of the members and magnetized in its thickness direction and thus parallel to the axes of the members to produce pole surfaces in the form of sectors of a circle, said permanent magnet portion being constituted of a high coercive force material and being substantially nondemagnetizable, the other of said members comprising a pair of substantially fiat members of soft ferromagnetic material mounted at right angles to the axes of said members and adjacent a pole surface of the permanent magnet portion, a winding on a reduced portion of at least one of said soft ferromagnetic members, said one soft ferromagnetic member having a portion intermediate said reduced portion and a portion remote therefrom of greater thickness than said reduced and remote portions, said rotor and stator members being rotable relative to one another about their axes whereby interaction may occur between the field produced by the permanent magnet and the winding on the soft ferromagnetic member.

4. Electrical appartus as set forth in claim 2 wherein the pair of soft ferromagnetic members are provided on opposite sides of the permanent magnet portion, each of said soft ferromagnetic members having a winding associated therewith.

5. Electrical apparatus comprising, in axially-arranged order, a first flat soft ferromagnetic member, a fiat circular permanent magnet spaced by a small air-gap from the soft member, and a second flat soft ferromagnetic member spaced by a small air-gap from the permanent magnet, said permanent magnet being substantially nondemagnetizable and being axially magnetized in its thickness direction to produce on opposite surfaces facing the soft members at least one pair of opposite poles, a portion on each of said soft members being of reduced area, and a winding on each of said reduced area portions, said soft members and said permanent magnet extending in planes at right angles to their axes and being rotatable relative to one another about their axes to enable interaction therebetween.

6. Electrical apparatus comprising, in axially-arranged order, a first flat circular permanent magnet, a first fiat soft ferromagnetic member spaced by a small air-gap from the first magnet, a second flat soft ferromagnetic member, and a second flat circular permanent magnet spaced by a small air-gap from the second soft member, said permanent magnets being substantially non-demagnetizable and being axially magnetized in their thickness direction to produce at least one pair of opposite poles in the form of sectors of a circle on their surfaces facing the soft members, adjacent portions on each of said soft members being of reduced area, and a winding on both of said reduced area portions, said soft members and magnets extending in planes at right angles to their axes and being rotatable relative to one another about their axes to enable interaction therebetween.

7. Electrical apparatus comprising axially-arranged, axial air-gap spaced rotor and stator members, one of said members including a flat, circular permanent magnet portion mounted at right angles to the axes of the members and magnetized in its thickness direction and thus parallel to the axes of the members to produce pole surfaces, said permanent magnet portion being constituted of a high coercive force material and being substantially non-demagnetizable, the other of said members comprising a substantially fiat circular member of soft ferromagnetic material mounted at right angles to the axes of said members and adjacent a pole surface of the permanent magnet portion, said soft member having a plurality of circularly-arranged spaced reduced area portions between which portions of increased thickness exist, a winding on each reduced area portion of said soft ferromagnetic member, said rotor and stator members being rotatable relative to one another about their axes whereby interaction may occur between the field the soft ferromagnetic member.

5 8. Electrical apparatus as set forth in claim 7 wherein 2,334,157 the soft ferromagnetic member has an annular shape, 2,637,839 said member being constituted of a plurality of concentric laminations.

References Cited in the file of this patent UNITED STATES PATENTS 613,209 Le Blanc Oct. 25, 1898 6 Marath Nov. 9, 1943 Piety May 5, 1953 FOREIGN PATENTS France Apr. 29, 1935 

